From TM Wiki

Your ladder position is based on who you beat when you are in Official Mode. Beating a player with a high ranking will award more points then a player who is below you. Each game has a separate ladder.

TMO & TMS have a ladder where you can loose points with a poor race finish, unlike TMN where you can only gain points.

Ladder stats can be found at..
TMO http://www.trackmania.com/rankings.php
TMS http://www.trackmaniasunrise.com/rankings.php
TMN http://www.trackmanianations.com/rankings.php